IAEA International Atomic Energy Agency
Biological Effects of Ionizing Radiation
Miroslav Pinak
&
Michael Hajek Radiation Safety and Monitoring Section
Division of Radiation, Transport and Waste Safety
Department of Nuclear Safety and Security
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Outline
• Introduction and historical background
• Targets for biological radiation damage
• Deterministic and stochastic effects
• ICRP system of radiological protection
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Ionizing Radiation
• Ionizing radiation
− Composed of particles that individually carry enough kinetic energy to liberate
an electron from an atom or molecule
− Kinetic energy > 12.4 eV
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Non-ionizing radiation Ionizing radiation
Ionization energy of soft tissue
12.4 eV or 100 nm
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Discovery of Ionizing Radiation
X-rays (1895) Natural radioactivity (1896)
Wilhelm Conrad Roentgen Antoine Henri Becquerel
Nobel Prize in Physics 1901 Nobel Prize in Physics 1903
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First Medical Observations
• Skin-burn attributed to radiation ─ 1901
• Radiation-induced leukaemia ─ 1911
• Clinical syndrome following exposure to atomic bomb explosions ─ 1946 P. D. Keller, J. Am. Med. Assoc. 131, 504 (1946).
• Holzknecht’s chromoradiometer related to skin erythema ─ 1902
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Targets for Biological Radiation Damage
• Human tissues are formed from cells that are grouped into organs and
systems of the body to perform the many specialized functions
• Each cell is defined by a membrane enclosing
− Cytoplasm containing up to 85% water
− Structures such a nucleus
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Chromosomes and DNA
• Chromosomes are organized structures of supercoiled deoxyribonucleic
acid (DNA) and proteins found in cells
• DNA macromolecules encode genetic information used in development
and functioning of all known living organisms
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Direct and Indirect Radiation Effects
• Indirect action predominant with low-LET radiation (X- and gamma rays)
• Direct action predominant with high-LET radiation (alpha particles)
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Consequences of DNA Damage
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DNA damage
Mutation Cell death Repair
Stochastic effect Deterministic effect Viable cell
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Deterministic Radiation Effects
• Occur at high doses when enough cells in an organ or tissue are killed
or prevented from functioning normally
− Threshold dose, above which effects are clinically observable
− Severity increases with dose
− Acute effects, non-malignant late effects
− Examples: Cataracts, erythema, acute radiation syndromes (ARS)
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DOSE
SE
VE
RIT
Y 100%
Threshold
dose
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Organ or tissue Acute dose (Gy) Type of effect Time of occurrence
Bone marrow 1 ARS 1 to 2 months
Skin 3 Erythema 1 to 3 weeks
Thyroid 5 Hypothyroidism ≥ 1 year
Lens of the eye 2 Cataract ≥ 6 months
Gonads 3 Permanent sterility Several weeks
Foetus 0.1 Teratogenesis ─
Deterministic Radiation Effects
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Deterministic Effects after Chernobyl
Chernobyl experience
− ARS and radiation burns
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Stochastic Radiation Effects
• Occur at all dose levels as a result of damage to the DNA
− Random or non-threshold effects
− Probability of occurrence increases with dose
− Late effects, often decades after exposure
− Examples: Radiation-induced cancers, hereditary effects
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DOSE
RIS
K
Linear-no-threshold
hypothesis
Quadratic
response
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Stochastic Radiation Risks
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DOSE
RIS
K
Risk factor
Relationship
is irrelevant
Background
incidence
Background
dose
Average 2.4 mSv
Typical 10. mSv
High 100. mSv
Increment of dose
Increment of
probability
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ICRP Nominal Risk Coefficients
• ICRP detriment-adjusted nominal risk coefficients (10−2 Sv−1) for
stochastic effects after exposure to radiation at low dose rate
Combined detriment due to excess cancer and hereditary effects
~ 5% per Sv
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Exposed population Cancer Hereditary effects Total
Publ.103 Publ. 60 Publ.103 Publ. 60 Publ.103 Publ. 60
Whole 5.5 6.0 0.2 1.3 5.7 7.3
Adult 4.1 4.8 0.1 0.8 4.2 5.6
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ICRP System of Radiological Protection
… to contribute to an appropriate level of protection for people and
the environment against the detrimental effects of radiation exposure ...
• Justification
− Any decision that alters the radiation exposure situation should do more good
than harm.
• Optimization (ALARA)
− The likelihood of incurring exposure, the number of people exposed, and the
magnitude of their individual doses should all be kept as low as reasonably
achievable, taking into account economic and societal factors.
• Limitation
− The total dose to any individual from regulated sources in planned exposure
situations other than medical exposure of patients should not exceed the appropriate
limits specified by the Commission.
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Philosophy of Individual Dose Limitation
• Prevention of deterministic effects
− Dose limits lower than threshold
• Reduction of stochastic effects to acceptable level
− Comparison with risks for other occupations
− Ethical judgment
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Annual dose limits
• Occupational exposure → 20 mSv (whole-body exposure)
→ 20 mSv (lens of the eye), 500 mSv (extremities)
• General public → 1 mSv (whole-body exposure)
→ 15 mSv (lens of the eye), 50 mSv (skin)
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Further Information
• IAEA Safety Standards
− No. GSR Part 3 (Interim) “Radiation Protection and Safety of Radiation Sources:
International Basic Safety Standards” (2011)
• IAEA Safety Standards Series
− No. SF-1 “Fundamental Safety Principles” (2006)
− No. RS-G-1.1 “Occupational Radiation Protection” (1999)
• Practical Radiation Technical Manuals
− “Health Effects and Medical Surveillance” (2004)
− “Personal Protective Equipment” (2004)
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Thank you for your kind attention!
Michael HAJEK | External Dosimetry Specialist | Radiation Safety and Monitoring Section | Division of Radiation, Transport and Waste Safety | Department of Nuclear Safety and Security | International Atomic Energy Agency | Vienna International Centre, PO Box 100, 1400 Vienna, Austria | Email: [email protected] | T: (+43-1) 2600-22712 | F: (+43-1) 26007-22712 | Follow us on www.iaea.org
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